Typical examples of electrochemical devices include condensers, capacitors, and batteries. These electrochemical devices have recently been used in many fields, including automotive equipment, renewable energy-related equipment, such as wind power generation and photovoltaic power generation, and communication devices, such as smart meters. It is expected that the market will grow continuously.
There is a demand for electrochemical devices with further improved charge-discharge characteristics, output characteristics, and cycle life. As a means to satisfy the demand, it is effective to reduce the resistance of electrochemical devices. High resistance in charging or discharging results in an increased loss due to the resistance. The loss generates heat, which directly affects the life. Because less heat generation results in a longer life, there is a growing demand for lower resistance.
Various components, such as electrode materials and electrolytic solutions, are actively improved to reduce the resistance of electrochemical devices. There is also a strong demand for separators with lower resistance.
Main functions of separators in electrochemical devices are separation of electrode foils and holding of electrolytic solution. For separation of electrode foils, separators should have low resistance and denseness. Materials for separators need electrical insulating properties and require hydrophilicity and lipophilicity to hold various electrolytic solutions. Poor wettability of separators not only results in low productivity of electrochemical devices but also makes it difficult to hold an adequate amount of electrolytic solution, thus shortening the lives of the electrochemical devices.
Thus, separators for electrochemical devices need to have low resistance, denseness, and high wettability by electrolytic solutions.
Separators for electrochemical devices described below have been proposed (see Patent Literature 1 to Patent Literature 7, for example).